Leptospirosis is an infectious disease caused by bacteria from the genus Leptospira. The disease occurs in a variety of different animals and in humans. In cattle, leptospirosis can be chronic or acute. Chronic disease is generally caused by Leptospira that have “adapted” to cattle as a host. Cattle are said to be maintenance hosts for the cattle-adapted organisms. Chronic disease can manifest itself as abortions, stillbirths or birth of weak calves. Infertility may be a problem in chronically infected herds. Cattle infected with the host-adapted Leptospira may not completely clear the organisms from their bodies.
In contrast to chronic disease, acute disease is generally caused by Leptospira for which cattle are non-maintenance or incidental or hosts. Although symptoms of acute disease are generally severe, and in calves can be fatal, the leptospire organisms responsible are normally cleared from the bodies of animals that survive the disease.
Although there are over 200 pathogenic serovars of leptospires, five serovars, hardjo, pomona, grippotyhposa, icterohaemorrhagiae and canicola, are generally associated with cattle. Two of these serovars, hardjo and pomona, are generally associated with chronic disease, Hardjo serovars exist in two different species of Leptospira. Serovar hardjo, type hardjo-bovis is in the genus Leptospira, species borgpetersenii (referred to as L. hardjo-bovis). Type hardjo-bovis appears to be the major cause of chronic leptospirosis in cattle in the United States. Serovar hardjo, type hardjo-prajitno is in the genus Leptospira, species interrogans. 
Compositions and methods that stimulate immune responses effective against Leptospira in cattle are known. However, attempts to stimulate protective and long-lasting immune responses can be less than satisfactory.